Project Summary Mller glia of cold-blooded vertebrates can re-enter the cell cycle and rise to photoreceptors following retinal injury, while mammals have lost this ability. As part of the NEI Audacious Goals Initiative, we have conducted a comprehensive analysis of injury-induced changes in gene expression and chromatin accessibility in zebrafish, chick and mouse M ller glia, allowing us to identify both evolutionarily conserved and species-specific gene regulatory networks that regulate glial reprogramming. This has identified a set of dedicated gene regulatory networks in mice that restrict proliferative and neurogenic competence in M ller glia. We aim to use these findings to gain a more complete insight into the molecular mechanisms that regulate neurogenic competence in mammalian M ller glia, and to develop treatments that can maximize generation of glial-derived photoreceptors while simultaneously not depleting the number of existing glia. To do this, we propose to generate individual loss of function mutants of the top candidate negative regulators of proliferative and neurogenic competence using AAV-mediated CRISPR/Cas9 gene disruption. We will first validate efficacy of sgRNAs targeting individual TFs, comprehensively profile changes in gene expression in reactive M ller glia following loss of function of these genes, and characterize the fate of M ller glia-derived cells. We will then conduct combinatorial loss of function of negative regulators of M ller glia reprogramming to enhance generation of glial-derived retinal progenitor cells in wildtype and Nfia/b/x-deficient mice. Finally, we will combine CRISPR- mediated loss of function analysis with overexpression of Ascl1, Crx and Nrl to enhance generation of M ller glia-derived rod photoreceptors in both wildtype and dystrophic retina. We predict that these studies may substantially advance cell-based regenerative treatments aimed at restoring retinal photoreceptors lost due to blinding diseases.